1. Field of the Invention
The present invention relates to a recording disc, and a recorded information reproducing apparatus and method for reproducing recorded information from the recording disc.
2. Description of Related Art
Today, DVD-ROM is widely used as a read-only optical recording medium which has previously recorded thereon information data such as audio, video, computer data and the like. The DVD-ROM has, for example, a two-layer recording surface comprised of a first recording layer and a second recording layer. When viewing the first recording layer from the top layer from which a reading beam light is irradiated onto the DVD-ROM, a recording pit train carrying information data is formed on a spiral or concentric track. On the other hand, when viewing the second recording layer from the bottom surface of the DVD-ROM, a recording pit train carrying information data is formed on a spiral or concentric track. Specifically, when viewing the first and second recording layers from the top surface of the DVD-ROM, convex recording pits are formed in the first recording layer, while concave recording pits are formed in the second recording layer. For this reason, the recording pits recorded in the first recording layer are hereinafter referred to as the “convex recording pits,” while the recording pits recorded in the second recording layer to the “concave recording pits.”
A conventional reproducing apparatus for reproducing recorded information from the DVD-ROM conducts a tracking servo in accordance with a DPD (Differential Phase Detection) scheme. In the DPD-based tracking control, reflection from the recording disc irradiated with a beam light is individually received by four photodetectors 20a–20d, arranged in a manner as illustrated in FIG. 1, which opto-electrically transduce the reflection into read signals Ra−Rd which are used in the tracking control. Then, these read signals Ra−Rd are used in the following calculations to generate a high frequency signal and a diagonal differential signal. The difference in phase between the two signals is used as an error signal for conducting the tracking control:High Frequency Signal=Ra+Rb+Rc+Rd Diagonal Differential Signal=(Ra+Rc)−(Rb+Rd)
The employment of the DPD scheme results in the satisfactory tracking control both for the first recording layer in which convex recording pits are recorded and for the second recording layer in which concave recording pits are recorded.
On the other hand, a writable recording disk such as DVD-R or DVD-RW is previously formed with a recording track which has a wobble pattern corresponding to disc addresses indicative of positions on the disc. A recorded information reproducing apparatus for recording and reproducing information data to and from the DVD-R or DVD-RW reads the wobble pattern on the recording track formed on the recording disc to recognize the position on the disc, while information data is being recorded. In this event, a push-pull signal is used for reading the wobble pattern on the recording track. The push-pull signal is generated in accordance with the following calculation using read signals Ra−Rd which are generated by four photodetectors 20a–20d as illustrated in FIG. 1 which individually receive and opto-electrically transduce reflected light from the disc:Push-Pull Signal=(Ra+Rb)−(Rc+Rd)
In addition, the recorded information reproducing apparatus conducts a tracking servo based on the push-pull signal. Specifically, the recorded information reproducing apparatus for recording and reproducing information data to and from a recording disc such as DVD-R or DVD-RW acquires disc addresses corresponding to the wobble pattern on the recording track based on the push-pull signal while conducting the tracking control.
Thus, the conventional recorded information reproducing apparatus which supports any of DVD-R, DVD-RW and DVD-ROM comprises dedicated processing circuits for generating the push-pull signal, high frequency signal and diagonal differential signal, respectively, resulting in an extremely large scale of the apparatus. There has been therefore a need for a recorded information reproducing apparatus which only requires the push-pull signal to conduct the tracking servo for any of DVD-R, DVD-RW and DVD-ROM.
However, the push-pull signal generated when the convex recording pit train is read from the first recording layer of the DVD-ROM as mentioned above is opposite in polarity to the push-pull signal generated when the concave recording pit train is read from the second recording layer. As such, for reproducing recorded information from the DVD-ROM, information data is first read from a recording layer intended for reproduction on a trial basis. In this event, when an appropriate tracking control is failed, the polarity of the push-pull signal is reversed, followed by a repetition of the read operation again from the initial position.
Therefore, the read operation may not be immediately started in some cases when the tracking control is conducted using the push-pull signal for a multi-layer recording layer which has a recording layer having a convex recording pit train recorded therein and a recording layer having a concave recording pit train recorded therein, or for a single-layer recording disc on which no recording pits are defined in a convex or concave shape.